1. Field of the Invention
The present invention relates to a method of influencing the strip contour in the edge region of a rolled strip in which by superimposing a conventional CVC contour the harmful side effect of a unilaterally narrowing roll on the body portion of the roll gap is compensated.
2. Description of the Related Art
When rolling flat strips, the conventional tapered roll with unilateral conical shape serves to influence the strip contour in the edge area of a rolled strip. Consequently, the tapered portion of the work roll is positioned in the vicinity of the strip edge in such a way that the tapered portion follows the strip edge.
Especially in a hot-rolling program, strips of different widths are rolled and the rolling schedules are increasingly put together more freely. In addition, when used in a cold rolling train, it is desired to use, if possible, only one roll type for different rolling stock widths and rolling conditions.
When using the conventional tapered roll, edge conditions result at various widths, wherein the narrowing roll end is pushed more or less far underneath the back-up roll, while the back-up roll remains unchanged in its horizontal position. Because of the different frictional engagement between the work roll and the back-up roll in axial direction, changes occur with respect to the load distribution as well as flattening between back-up roll and work roll as well as the bending behavior of the roll set and, thus, the profile of the roll gap is influenced. This results in undesirable profile shapes and non-planarities of the rolling stock. In addition, other influencing values, such as, rolling force, thermal crown, etc., additionally influence the elastic behavior of the entire roll set.
Therefore, in order to ensure the strip quality or strip planarity, it is necessary to use additional adjusting means, such as work roll bending means or rolling force redistributing means. However, these measures known in the prior art frequently are not sufficient for meeting the increased requirements especially with respect to the planarity also under extreme edge conditions. When manufacturing hot-rolled strip, these requirements are particularly the ability of putting together rolling schedules with more flexibility, wherein, in addition to increased thicknesses and material changes, especially sudden jumps toward narrow and wide strips are desired (mixed rolling).
It is known from DE 30 38 865 C1 to compensate changes of the thermal crown and the work roll wear by suitable adjusting means, such as displacement means and/or bending means, for example, CVC displacement (continuously variable crown displacement) or a suitable cooling.
For controlling the camber and/or edge drop of rolled strip, it is known from EP 0 276 743 B1 to adjust the horizontal displacement of the work rolls and the bending forces acting on the work rolls of a group of roll stands of a tandem rolling mill arranged upstream in accordance with the rolling conditions including the width of the strips.
DE 22 06 912 C3 proposes in six-high stands to construct the intermediate rolls in adaptation to the rolling stock width in such a way that one end of the effective roll body of the upper intermediate roll is located in the area of one rolling stock edge and the opposite end of the effective roll body of the lower intermediate roll is located in the region of the lower rolling stock edge, so that each work roll has an end portion which is free of pressure from the corresponding intermediate roll, wherein roll bending devices act on the ends of the work rolls. The rolls are ground with symmetrical cambers in the conventional manner, or roll bending devices are provided. An end portion of each intermediate roll is constructed so as to be conically narrowing over a relatively short length, which has the disadvantage that a sudden change of the load distribution occurs in the area of the transition from the effective roll body to the conical portion.
DE 22 60 256 C2 discloses a roll stand with devices for axially displacing the work rolls in opposite directions when changes of the rolling stock width occur, so that always one end of the work surface of a work roll is held between a rolling stock edge and the end of the corresponding back-up roll. Moreover, intermediate rolls are provided, wherein the upper intermediate roll is displaceable in the same direction as the lower work roll and the lower intermediate roll is displaceable in the same direction as the upper work roll. Also in this case, only a conical narrowing of the ends of the intermediate rolls is provided, which has the disadvantageous effects described above.